An evaluation of morningness and schedule misfit using the revised Preferences Scale (PS-6): Implications for work and health outcomes among healthcare workers.

The last several decades of shift work tolerance and circadian misalignment research has had mixed results regarding the adverse impact of shift work on work and health outcomes. This inconsistency is, in part, due to the circadian typology measure employed and the study methodology. Based on models of shift work and health, the present study examined associations between circadian misalignment, end-of-day strain, and job- and health-related outcomes using the revised Preferences Scale (PS-6). A sample of 129 healthcare workers (76.7% female) from the United States (67%) and Australia (34.1%) aged 22 to 64 responded to a self-report questionnaire on work schedules, work stressors, and well-being. Multiple regression analysis found that the preferences for cognitive activity subscale of the PS-6 moderated the association between shift work and strain (b = -.36, p < .001). Those who worked nights experienced more strain if their preferences for cognitive activity were misaligned, whereas no differences in strain were observed among day workers. Moderated-mediation analyses, on the basis 95% confidence intervals, found that shift work had a conditional indirect effect on work-family conflict, job satisfaction, and health-related quality of life, via strain, and the effect was moderated by preferences for cognitive activity. Findings provide additional evidence for the criterion and external validity of the PS-6, and importantly, the present study establishes further support for models of shift work and health. Overall, the analyses highlight the importance of exploring the interactions between shift work and different dimensions of morningness in shift work tolerance research.

More Than Morningness: The Effect of Circadian Rhythm Amplitude and Stability on Resilience, Coping, and Sleep Duration.

Self-report tools that measure circadian rhythms have focused primarily on phase. We add to the sparse literature on assessing amplitude and stability. We randomly recruited 1,163 participants who completed several measures. The correlation between the LV scale (amplitude) and FR scale (stability) was -0.12 (p < 0.01). As expected, amplitude was negatively associated with phase (r = -0.64, p < 0.01) while stability showed a weak link with phase (r = 0.07, p < 0.05). Structural equation modeling suggested a close model-fit of the factor structure in the sample (RMSEA = 0.033). The LV scale explained 22% of the variance, while the FR scale explained 23%. Scale reliability was satisfactory for the LV scale (0.68) and good for the FR scale (0.73). Participants with low amplitude or flexible rhythms reported significantly better resilience, coping, and required less daily sleep. We constructed a composite circadian categorical variable to combine the best attributes from the LV and FR scales; participants with both low amplitude and flexible rhythms, reported significantly better resilience, coping, and less sleep need. We found rhythm amplitude decreased with age, while stability remained constant.

Animal Welfare Attitudes: Effects of Gender and Diet in University Samples from 22 Countries.

Animal Welfare Attitudes (AWA) are defined as human attitudes towards the welfare of animals in different dimensions and settings. Demographic factors, such as age and gender are associated with AWA. The aim of this study was to assess gender differences among university students in a large convenience sample from twenty-two nations in AWA. A total of 7914 people participated in the study (5155 women, 2711 men, 48 diverse). Participants completed a questionnaire that collected demographic data, typical diet and responses to the Composite Respect for Animals Scale Short version (CRAS-S). In addition, we used a measure of gender empowerment from the Human Development Report. The largest variance in AWA was explained by diet, followed by country and gender. In terms of diet, 6385 participants reported to be omnivores, 296 as pescatarian, 637 ate a vegetarian diet and 434 were vegans (n = 162 without answer). Diet was related with CRAS-S scores; people with a vegan diet scored higher in AWA than omnivores. Women scored significantly higher on AWA than men. Furthermore, gender differences in AWA increased as gender inequality decreased.

Circadian preferences in young adults: Psychometric properties and factor structure of the Portuguese version of the Preferences Scale (PS-6).

Morningness is a trait-like variable which has been extensively studied within chronobiology. Despite the number of existing measures to assess morningness, there is a need for brief instruments that are psychometrically sound to be used in applied settings. Accordingly, the modified version of the Preferences Scale (PS-6) comprises six items and was reported to have adequate reliability and satisfactory validity indicators. In this article, the psychometric properties of the Portuguese version of the PS-6 are reported. A total of 700 students attending medical school were recruited, and this sample was randomly divided into two groups. In the first group (n = 352), we assessed the internal consistency calculations and conducted a principal component analysis of the posited structure. In the second group (n = 348), we conducted a confirmatory factor analysis (CFA) using structural equation modeling. Overall, the results indicated that the PS-6 has adequate reliability (α = .75) and is constituted by two components: (I) preferred cognitive activities timings and (II) preferred sleeping-eating timings, respectively. In conclusion, the Portuguese version of the PS seems suitable for use in research and applied settings such as shift work schedules management. However, the applicability of the PS-6 in other samples and further validity indicators should be both investigated. The use of actigraphy and biological measures should also be collected to enhance the robustness of the PS-6.

Predictors of shift work disorder among nurses: a longitudinal study.

BACKGROUND: Shift work is associated with sleep problems and impaired health. The main aim of the present study was to explore predictors of developing shift work disorder (SWD) among Norwegian nurses using a longitudinal design. METHODS: A total of 1533 nurses participating in a survey on shift work, sleep and health responded to questionnaires at baseline and at follow-up about two years later. SWD was defined as problems of excessive sleepiness and/or complaints of insomnia related to the work schedule. RESULTS AND CONCLUSIONS: There was a significant reduction (p < 0.001) in the prevalence of SWD from baseline to follow-up, from 35.7% to 28.6%. Logistic regression analyses showed significant risks of having SWD at follow-up and the following variables measured at baseline: number of nights worked the last year (OR = 1.01, 95% CI = 1.01-1.02), having SWD (OR = 5.19, 95% CI = 3.74-7.20), composite score on the Epworth Sleepiness Scale (OR = 1.08, 95% CI = 1.04-1.13), use of melatonin (OR = 4.20, 95% CI = 1.33-13.33), use of bright light therapy (OR = 3.10, 95% CI 1.14-8.39), and symptoms of depression measured by the Hospital Anxiety and Depression Scale (OR = 1.07, 95% CI = 1.00-1.14). In addition, leaving night work between baseline and follow-up was associated with a significantly reduced risk of SWD at follow-up (OR = 0.12, 95% CI = 0.07-0.22).

Cross-sectional associations between multiple lifestyle behaviors and health-related quality of life in the 10,000 Steps cohort.

BACKGROUND: The independent and combined influence of smoking, alcohol consumption, physical activity, diet, sitting time, and sleep duration and quality on health status is not routinely examined. This study investigates the relationships between these lifestyle behaviors, independently and in combination, and health-related quality of life (HRQOL). METHODS: Adult members of the 10,000 Steps project (n = 159,699) were invited to participate in an online survey in November-December 2011. Participant socio-demographics, lifestyle behaviors, and HRQOL (poor self-rated health; frequent unhealthy days) were assessed by self-report. The combined influence of poor lifestyle behaviors were examined, independently and also as part of two lifestyle behavior indices, one excluding sleep quality (Index 1) and one including sleep quality (Index 2). Adjusted Cox proportional hazard models were used to examine relationships between lifestyle behaviors and HRQOL. RESULTS: A total of 10,478 participants provided complete data for the current study. For Index 1, the Prevalence Ratio (p value) of poor self-rated health was 1.54 (p = 0.001), 2.07 (p≤0.001), 3.00 (p≤0.001), 3.61 (p≤0.001) and 3.89 (p≤0.001) for people reporting two, three, four, five and six poor lifestyle behaviors, compared to people with 0-1 poor lifestyle behaviors. For Index 2, the Prevalence Ratio (p value) of poor self-rated health was 2.26 (p = 0.007), 3.29 (p≤0.001), 4.68 (p≤0.001), 6.48 (p≤0.001), 7.91 (p≤0.001) and 8.55 (p≤0.001) for people reporting two, three, four, five, six and seven poor lifestyle behaviors, compared to people with 0-1 poor lifestyle behaviors. Associations between the combined lifestyle behavior index and frequent unhealthy days were statistically significant and similar to those observed for poor self-rated health. CONCLUSIONS: Engaging in a greater number of poor lifestyle behaviors was associated with a higher prevalence of poor HRQOL. This association was exacerbated when sleep quality was included in the index.

Associations between occupational indicators and total, work-based and leisure-time sitting: a cross-sectional study.

BACKGROUND: A better understanding of how occupational indicators (e.g. job type, doing shift-work, hours worked, physical demand) influence sitting time will aid in the design of more effective health behaviour interventions. The aim of the study was to examine the associations between several occupational indicators and total, occupational and leisure-time sitting. METHODS: Cross-sectional self-report data was collected in November 2011 from 1194 participants through a telephone interview in regional Queensland, Australia (response rate was 51.9%). The Workforce Sitting Questionnaire was used to measure sitting time. Multiple logistic regression was applied to examine associations between sitting time and occupational indicators. RESULTS: Of all participants 77.9% were employed full-time, 72.7% had white-collar jobs, 35.7% were engaged in shift-work, 39.5% had physically demanding jobs, and 53.2% had high total sitting time (>8 hours a day). Those in physically demanding and blue-collar occupations were less likely to report high total (physically demanding: OR = 0.41,95% CI = 0.29-0.58; blue-collar: OR = 0.55,95% CI = 0.37-0.82) and occupational (physically demanding: OR = 0.26,95% CI = 0.14-0.24; blue-collar: OR = 0.32,95% CI = 0.21-0.49) sitting time compared to those in physically undemanding and white-collar occupations respectively. Working more than 8 hours per day was inversely associated with high leisure-time sitting (OR = 0.44,95% CI = 0.29-0.68). No evidence for 'compensation' effects, where lower occupational sitting is compensated with higher leisure-time sitting, was found. CONCLUSIONS: Behaviour change interventions are needed to reduce sitting time as a means to prevent chronic disease. Workplace initiatives to reduce sitting time may be particularly important among individuals employed in white-collar and physical undemanding occupations, although other intervention strategies targeting leisure-time sitting are also required.

Reviewing the psychometric properties of contemporary circadian typology measures.

The accurate measurement of circadian typology (CT) is critical because the construct has implications for a number of health disorders. In this review, we focus on the evidence to support the reliability and validity of the more commonly used CT scales: the Morningness-Eveningness Questionnaire (MEQ), reduced Morningness-Eveningness Questionnaire (rMEQ), the Composite Scale of Morningness (CSM), and the Preferences Scale (PS). In addition, we also consider the Munich ChronoType Questionnaire (MCTQ). In terms of reliability, the MEQ, CSM, and PS consistently report high levels of reliability (>0.80), whereas the reliability of the rMEQ is satisfactory. The stability of these scales is sound at follow-up periods up to 13 mos. The MCTQ is not a scale; therefore, its reliability cannot be assessed. Although it is possible to determine the stability of the MCTQ, these data are yet to be reported. Validity must be given equal weight in assessing the measurement properties of CT instruments. Most commonly reported is convergent and construct validity. The MEQ, rMEQ, and CSM are highly correlated and this is to be expected, given that these scales share common items. The level of agreement between the MCTQ and the MEQ is satisfactory, but the correlation between these two constructs decreases in line with the number of "corrections" applied to the MCTQ. The interesting question is whether CT is best represented by a psychological preference for behavior or by using a biomarker such as sleep midpoint. Good-quality subjective and objective data suggest adequate construct validity for each of the CT instruments, but a major limitation of this literature is studies that assess the predictive validity of these instruments. We make a number of recommendations with the aim of advancing science. Future studies need to (1) focus on collecting data from representative samples that consider a number of environmental factors; (2) employ longitudinal designs to allow the predictive validity of CT measures to be assessed and preferably make use of objective data; (3) employ contemporary statistical approaches, including structural equation modeling and item-response models; and (4) provide better information concerning sample selection and a rationale for choosing cutoff points.

Shift work disorder in a random population sample--prevalence and comorbidities.

Few studies have investigated the presence of shift work disorder (SWD) in the general community. We addressed many of the limitations in this literature and present new findings. SWD has been treated as an 'all or none' construct but we propose the need to consider the 'severity' of the disorder. Using random digit dialling, we randomly recruited 1163 participants. Participants completed an extensive battery of scales and questions concerning work, health and individual differences. Three questions based on the criteria from the International Classification for Sleep Disorders were used to categorise participants with SWD (n = 176). In addition, we asked participants whether SWD interfered with aspects of their life and high ratings were used to define severe shift work disorder (SSWD). The prevalence of SWD was 32.1% among night workers and 10.1% in day workers (p<.001). SSWD was present in 9.1% of night workers and 1.3% of day workers (p<.001). Adjusted logistic regression analyses found significant associations between SWD and night work (OR = 3.35, CI 2.19-5.12), weekly work hours (OR = 1.02, CI 1.00-1.04), short sleep (≤ 6 h; OR = 2.93, CI 1.94-4.41), languidity (OR = 1.11, CI 1.06-1.16) and resilience (OR = 0.56, CI 0.43-0.81). Night work, short sleep, languidity, and hypertension were significantly associated with SSWD. Overall, participants with SSWD slept 0.80 h less than other participants (p<.001). Night work, short sleep and languidity were associated with both SWD and SSWD. Day workers with SWD symptoms reported significantly shorter sleep duration, higher levels of languidity and worked longer working hours compared to day workers without SWD.

The association between short sleep and obesity after controlling for demographic, lifestyle, work and health related factors.

OBJECTIVE: The relationship between short sleep and obesity remains unclear, and a possible explanation is that many studies have not included sufficient control variables in the analyses. We examined the association between sleep and being overweight or obese after adjusting for the confounding contributions of 17 variables. METHODS: A random sample of 1162 Australian adults from three regional cities in central Queensland, Australia, participated in a telephone survey. A series of increasingly complex multinomial logistic regression models were employed to assess the association between short sleep (< or = 6 h) being overweight (body mass index [BMI] 25-29.99 kg/m2) and obesity (BMI, > or = 30 kg/m2), while controlling for several demographic, lifestyle, work, and health-related variables. RESULTS: The results suggested obesity was significantly associated with short sleep, age, male gender, lower education level, less physical activity, more sitting time, working longer hours, drinking more alcohol, having diabetes mellitus (DM), and having hypertension. Being overweight was significantly associated with age, male gender, smoking, and working more than 43hours per week. CONCLUSIONS: After adjustment of several confounding variables, a significant association between short sleep and obesity was obtained, but there was no association between short sleep and being overweight. Additional studies applying comprehensive analytic models and stronger research designs are needed to confirm our findings.

The distribution of sleepiness, sleep and work hours during a long distance morning trip: a comparison between night- and non-night workers.

Few studies have examined the extent of driver sleepiness during a long distance morning trip. Sleepiness at this time may be high because of night work, waking early to commence work or travel, sleep disorders and the monotony of driving long distances. The objective of this study was to estimate the prevalence of chronic sleepiness (Epworth sleepiness score ≥10) and sleep restriction (≤5h) in a sample of 649 drivers. Participants driving between 08:00 and 10:00 on three highways in regional Australia participated in a telephone interview. Approximately 18% of drivers reported chronic sleepiness. The proportions of night workers (NW) and non-night workers (NNW) with chronic sleepiness were not significantly different but males reported a significantly greater proportion of chronic sleepiness than females. The NW group had a significantly greater proportion of drivers with ≤5h of sleep in the previous 24 and 48h, fewer nights of full sleep (≤4), acute sleepiness and longer weekly work hours. The NW group reported driving a significantly longer distance at Time 1 (Mean=140.29±72.17km, versus 117.55±89.74km) and an additional longer distance to complete the journey (Mean=89.33±95.23km, versus 64.77±94.07km). The high proportions of sleep restriction and acute sleepiness among the NW group, and the amount of chronic sleepiness in the NW and NNW groups reported during a long distance morning trip may be of concern for driver safety.

Further evidence for the influence of photoperiod at birth on chronotype in a sample of German adolescents.

Individuals differ in their circadian preferences (chronotype). There is evidence in the literature to support a season-of-birth effect on chronotype but the evidence is not convincing. In part, the relationship is obscured by a number of methodological differences between studies, including the measures used to define morningness, the way in which the seasons were categorized, and the sample size. This study adds to the literature in several ways. First, we adopt a new approach to categorizing the photoperiod rather than the calendar season; thus we prefer to use the term photoperiod at birth. Second, we used two measures of morningness. Third, we used a large and homogeneous German sample. The results show that adolescents (n = 2905) born during the increasing photoperiod (Feb-Apr) had a significantly later midpoint of sleep (MSFsc) than those born during the decreasing photoperiod (Aug-Oct). A similar pattern was found for the Composite Scale of Morningness (CSM). Furthermore, both measures of chronotype demonstrated a significant quadratic function over a 1-yr cycle. When looking at each of six consecutive years separately, the Composite Scale of Morningness suggests a cosine rhythm linked to increasing and decreasing photoperiods that becomes weaker in amplitude with increasing age. Despite the strengths in our study, the effect of photoperiod at birth on chronotype remains small. Future studies may require larger sample sizes, may need to explore how neonatal light exposure modulates chronotype, and may need to track how puberty and adolescent lifestyle habits mask the photoperiod effect.

Sleepiness, long distance commuting and night work as predictors of driving performance.

Few studies have examined the effect of working night shift and long distance commuting. We examined the association between several sleep related and demographic variables, commuting distance, night work and use of mobile phones on driving performance. We used a prospective design to recruit participants and conducted a telephone survey (n = 649). The survey collected demographic and journey details, work and sleep history and driving performance concerning the day the participant was recruited. Participants also completed the Karolinska Sleepiness Scale and the Epworth Sleepiness Scale. Night workers reported significantly more sleepiness, shorter sleep duration and commuting longer distances. Seven variables were significant predictors of lane crossing. The strongest predictor was acute sleepiness (OR = 5.25, CI, 1.42-19.49, p<0.01) followed by driving ≥150 kms (OR = 3.61, CI, 1.66-7.81, p<0.001), obtaining less than 10 hours sleep in the previous 48 hours (OR = 2.58, CI, 1.03-6.46, p<0.05), driving after night shift (OR = 2.19, CI, 1.24-3.88, p<0.001), being <43 years old (OR = 1.95, CI, 1.11-3.41, p<0.05) and using mobile phones during the journey (OR = 1.90, CI, 1.10-3.27, p<0.05). Sleep related variables, long-distance commuting and night work have a major impact on lane crossing. Several interventions should be considered to reduce the level of sleepiness in night workers.

Circadian typology: a comprehensive review.

The interest in the systematic study of the circadian typology (CT) is relatively recent and has developed rapidly in the two last decades. All the existing data suggest that this individual difference affects our biological and psychological functioning, not only in health, but also in disease. In the present study, we review the current literature concerning the psychometric properties and validity of CT measures as well as individual, environmental and genetic factors that influence the CT. We present a brief overview of the biological markers that are used to define differences between CT groups (sleep-wake cycle, body temperature, cortisol and melatonin), and we assess the implications for CT and adjustment to shiftwork and jet lag. We also review the differences between CT in terms of cognitive abilities, personality traits and the incidence of psychiatric disorders. When necessary, we have emphasized the methodological limitations that exist today and suggested some future avenues of work in order to overcome these. This is a new field of interest to professionals in many different areas (research, labor, academic and clinical), and this review provides a state of the art discussion to allow professionals to integrate chronobiological aspects of human behavior into their daily practice.

20th International Symposium on Shiftwork and Working Time: biological mechanisms, recovery, and risk management in the 24-h society.

This dedicated issue of Chronobiology International is devoted to the selected proceedings of the 20th International Symposium on Shift Work and Working Time held in Stockholm, Sweden, 28 June to 1 July 2011. It constitutes the fifth such issue of the journal since 2004 dedicated to the selected proceedings to the meetings of the Working Time Society. The key theme of the 20th Symposium was "Biological Mechanisms, Recovery, and Risk Management in the 24-h Society." The collection of papers of this dedicated issue represents the best of contemporary research on the effects of night and rotating shift schedules on worker health and safety. The contents cover such topics as sleep restriction, injuries, health, and performance of night work and rotating shiftwork, plus light treatment as a countermeasure against the circadian disruption of shiftwork. The majority of the papers are observational field studies, including some of large sample size, and three studies are well-designed laboratory experiments.

Season of birth and morningness: comparison between the northern and southern hemispheres.

The present study explored the possible role of the photoperiod at birth on morningness by collecting data in the northern (Italy) and southern (Australia) hemispheres. To assess circadian typology, the Composite Scale of Morningness (CS) was administered to a sample of 1734 university students (977 Italian and 757 Australian; 1099 females and 635 males; age 24.79 ± 7.45 yrs [mean ± SD]). Consistent with the literature, females reported higher CS scores (morningness) than males, and Australian participants reported higher CS scores than Italian participants. Allowing for the fact the seasons are reversed between the hemispheres, the results are in line with previous studies. The authors found more evening types were born during the seasons associated with longer photoperiod (spring and summer), and more morning types were born during the seasons associated with shorter photoperiod (autumn and winter), indirectly supporting an imprinting-like phenomenon played by the photoperiod at birth.

Demographic factors, fatigue, and driving accidents: An examination of the published literature.

This article reviews the literature pertaining to the association between demographic variables (e.g., age, sex, race, socio-economic status) with fatigue, and when feasible, accident risk. It also explores their potential influence and interaction with some working arrangements, commute time, personality characteristics, and circadian chronotype. Fatigue has been implicated in a range of impairments that can have detrimental effects on individuals, and it is differentially associated with conventional demographic variables. However, several major methodological limitations prevent clear conclusions. First, there is absence of a shared definition both within and across disciplines. Second, although fatigue has been investigated using a variety of diverse designs, they have either been too weak to substantiate causality or lacked ecological validity. Third, while both subjective and objective measures have been used as dependent variables, fatigue has been more often found to be more strongly linked with the former. Fourth, with the exception of age and sex, the influence of other demographic variables is unknown, since they have not yet been concomitantly assessed. In instances when they have been assessed and included in statistical analyses, they are considered as covariates or confounders; thus, their contribution to the outcome variable is controlled for, rather than being a planned aspect of investigation. Because the interaction of demographic factors with fatigue is largely a neglected area of study, we recommend greater interdisciplinary collaborations, incorporation of multiple demographic variables as independent factors, and use of within-participant analyses. These recommendations would provide meaningful results that may be used to inform public policy and preventive strategies.

Sleep disorders, medical conditions, and road accident risk.

Sleep disorders and various common acute and chronic medical conditions directly or indirectly affect the quality and quantity of one's sleep or otherwise cause excessive daytime fatigue. This article reviews the potential contribution of several prevalent medical conditions - allergic rhinitis, asthma, chronic obstructive pulmonary disease, rheumatoid arthritis/osteoarthritis - and chronic fatigue syndrome and clinical sleep disorders - insomnia, obstructive sleep apnea, narcolepsy, periodic limb movement of sleep, and restless legs syndrome - to the risk for drowsy-driving road crashes. It also explores the literature on the cost-benefit of preventive interventions, using obstructive sleep apnea as an example. Although numerous investigations have addressed the impact of sleep and medical disorders on quality of life, few have specifically addressed their potential deleterious effect on driving performance and road incidents. Moreover, since past studies have focused on the survivors of driver crashes, they may be biased. Representative population-based prospective multidisciplinary studies are urgently required to clarify the role of the fatigue associated with common ailments and medications on traffic crash risk of both commercial and non-commercial drivers and to comprehensively assess the cost-effectiveness of intervention strategies.

A psychometric assessment of the Circadian Amplitude and Phase Scale.

The Circadian Amplitude and Phase Scale (CAPS) is a new self-report tool that aims to assess amplitude and phase. The CAPS consists of three factors made up of 38 items. Amplitude is posited to be assessed via two of these factors: time awareness (TA) and/or strength of preference (SOP). The remaining factor, phase, is assessed via the existing Preferences Scale (PS). Given there is no published research using this measure, the authors undertook two studies to examine its psychometric properties and construct validity. In a sample of 351 North American students, the authors identified a three-factor 34-item model using principal components analysis. The components explained 39% of the variance, and scale reliability ranged from 0.73 (SOP) to 0.88 (PS). The correlations between the components were small, suggesting they are each assessing different constructs. Thus, it is unlikely TA and SOP may both be indicators of amplitude. The distributions for each scale were divided into two groups (≤ 25th and ≥ 75th percentiles), and these groups were used to assess construct validity using alertness ratings by time-of-day. The results from a multivariate general linear model indicated a significant difference (p < .001) in sleepiness ratings by time-of-day for the PS scale only. In the second study, the authors applied confirmatory factor analysis in an attempt to replicate the factor structure identified in the student sample in a working sample (n = 388). The results suggested the model fit was not optimal. Subsequent analysis suggested a 26-item model was a better fit, but it also was not optimal. The intercorrelations between the factors were larger than in the student sample but again small, indicating the constructs are independent measures. The inability to replicate the factor structure is most likely explained by the differences in the sample characteristics of age, sex, and perhaps difficulty in interpreting the items. The limitations of these studies are discussed and recommendations for future studies are made.

Introductory Overview--19th International Symposium on Shiftwork and Working Time: Health and Well-being in the 24-h Society.

This dedicated issue of Chronobiology International comprises the partial proceedings of the "19th International Symposium on Shiftwork and Working Time" held August 2009 in Venice, Italy. The key theme of the symposium was "Health and Well-being in the 24-h Society." The topics covered by the 19 peer-reviewed original research papers address the direct and indirect effects of working time arrangement on the circadian system, sleep, performance, safety, and well-being, i.e., work-family conflict, work-ability, and depression--topics that are consistent with the scope of the Journal. The laboratory-based studies utilize well-designed protocols, and the survey studies constitute representative and large sample sizes. This issue builds upon the tradition established by the Journal commencing with the publication in 2004 of the proceedings of the "16th International Symposium on Shiftwork and Working Time" and the three symposia on shiftwork and working hours published thereafter by the Journal.